Starters for prime movers such as gas turbines



Jan. 1, 1957 D. F. WELCH ET AL 2,775,865

STARTERS FOR PRIME MOVERS SUCH AS GAS TURBLNES Filed June 4, 1952 PR/ME Mam? J7ZM77A/G MECHANISM nvvzwroms 00064196 red/ya: WELCH Ava/4P0 flLLfiN 55. .4.

United States Patent STARTERS FOR PRIME MOVERS SUCH AS GAS TURBINES Douglas Francis Welch, Thurlaston, near Rugby, Richard Allan Bell, Rugby, and Kenneth Barrington Randall, Coventry, England, assignors to The British Thomson- Houston Company Limited, a British company Application June 4, 1952, Serial No. 291,618

Claims priority, application Great Britain June 7, 1951 2 Claims. (Cl. 6039.14)

This invention relates to starting apparatus for prime movers such as gas turbines and the like and is more particularly directed to improved apparatus for starting a gas turbine having a turbine starter.

Turbine starters are well-known, being used extensively for the starting of internal combustion engines and gas turbines, the starter uses a gaseous fluid derived from the burning of cordite or similar solid fuel cartridges. It has been found that these cartridges are not entirely satisfactory for use in starters fitted to certain modern engines in that the engines per se may have a very high inertia requiring a sustained fluid flow through the starter and though the cartridge may be able to adequately supply this, the carrying of spare cartridges, the weight of such cartridges and the inaccessibility of the starter in many installations militate against their use.

It has been suggested that cartridges be replaced by a liquid fluid in the form of a monofuel. By the term monofuel we mean any fuel which does not require external oxygen for decomposition. Such a monofuel, for example, is propyl nitrate (CsHqNOs) which is known under the registered trademark Catalene.

Various technical difficulties are associated with the initiation of the decomposition of a monofuel, and the satisfactory supply of the decomposed fluid to the starter. We have found that the admixture of the monofuel and air ignited by a spark to initiate decomposition is undesirable, unreliable and at times dangerous, and to overcome the disadvantage of such a method we have adopted an apparatus Which obviates the need of an admixture of air and monofuel.

It has been proposed to provide apparatus for starting a prime mover such as a gas turbine having a turbine starter wherein a monofuel as hereinbefore defined is sprayed into a substantially closed reaction chamber provided with an outlet nozzle, self-sustained decomposition of the monofuel being induced by a heating means which causes gasification of the monofuel spray and brings it to the minimum temperature and pressure for the said decomposition to be sustained, an exothermic reaction taking place which provides a supply of gas for the turbine starter to effect starting of the said prime mover.

It has also been proposed to provide apparatus for starting a prime mover such as a gas turbine having a turbine starter wherein a monofuel as hereinbefore define is sprayed into a substantially closed reaction chamber provided with an outlet nozzle, self-sustained decomposition of the monofuel being induced by a heating means which causes gasification of the monofuel spray and brings it to the minimum temperature and pressure for the said decomposition to be sustained, the heating means being then shut off and an exothermic reaction taking place which is utilised to decompose an additional supply of monofuel and thereby provide a supply of gas to the turbine starter to etfect starting of the said prime mover.

Further, it has been proposed that the reaction chamber may be an auxiliary chamber, the outlet nozzle being in communication with a main chamber larger in volume than the auxiliary chamber, the main chamber having an outlet nozzle to the turbine starter and provided with its own supply of monofuel, that is, the additional supply of monofuel referred to above, the basic minimum conditions for decomposition of the monofuel being etfected in the said auxiliary chamber so that when the fluid enters the larger volume of the main chamber it is at a temperature and pressure slightly above the basic minimum requisite for decomposition of the monofuel in the main chamber thereby permitting monofuel to be fed directly to the main chamber for decomposition and thence to the turbine starter.

According to the present invention we provide an intermediate chamber, that is to say a chamber intermediate the auxiliary chamber and the main chamber, the decomposed fuel in the auxiliary chamber being fed into the intermediate chamber where it effects decomposition of monofuel supplied to the intermediate chamber, the decomposed fuel being then fed into the main chamber to promote decomposition of monofuel supplied to the said main chamber, the main chamber being provided with an outlet nozzle to the turbine starter.

It is known that using a monofuel such as propylnitrate the correct conditions which must exist in the reaction chamber for self-sustained decomposition of the propyl-nitrate are the following basic minima:

Pressure in reaction chamber, approximately 100 p. s. i. Temperature in reaction chamber, approximately 400 C.

We therefore arrange a heating means in the reaction chamber and it will readily be appreciated that the heating means must provide sufficient heat to raise the liquid monofuel to boiling point, change the liquid to vapour and raise the vapour to the necessary temperature for decomposition. The evaporation must also pass the outlet nozzle at a suflicient rate to maintain the necessary minimum pressure.

Under practical conditions the size of the nozzle connecting the reatcion chamber to the turbine starter is governed by the requirements of the starter and prime mover in question and the decomposition pressure.

The maximum power dissipation of the heating means will almost certainly be limited by the capacity of the storage battery where the prime moved is a gas turbine for aircraft and the like.

When starting aircraft gas turbines it is moreover essential that the start be achieved in the shortest possible time, usually in a matter of seconds.

To keep the time required to initiate decomposition of a monofuel by means of a heater means to a minimum, the following conditions must be met:

(a) Outlet nozzle orifice area from the reaction chamber should be kept to a minimum;

(b) Power dissipation of the heating means should be the maximum possible.

However, both the above conditions are limited and as it was obvious that the power available for the correct conditions could not be obtained against the full size outlet nozzle, some means of reducing the power required was sought. This we have done by introducing an auxiliary chamber which acts as a small reaction chamber having a small area outlet nozzle communicating with a main chamber, the monofuel in the auxiliary chamber being raised to basic minimum decomposition conditions for the monofuel and subsequently raised to full working pressure, and upon being fed into the larger volume main chamber the conditions in the main chamber are arranged to be the required basic minimum for decomposition of monofuel supplied to the main chamber per se.

It can be seen that if the reaction chamber, i. e. the chamber containing the heating element, is allowed to feed an intermediate chamber which itself feeds a main chamber, then an even quicker start will be obtained, since the volume and outlet nozzle diameter of the intermediate chamber would now be approximately the same as those of the reaction chamber, that is to say an auxiliary chamber, and the size of the auxiliary chamber and the diameter of its outlet nozzle could be very much smaller than this. It will be appreciated that decided advantages accrue from the use of a coil heating means within the reaction chamber in that the coil is only in the hot zone of the reaction chamber for a small period of time; whereas if it were placed in the main chamber it would be in the hot zone of the main chamber for the entire period of the starting operation, and this would have a deleterious effect upon the coil.

As an example, suppose that the maximum working pressure of all three chambers, i. e. the auxiliary reaction chamber, the intermediate chamber and the main chamber, is 800 p. s. i. and that the basic minimum pressure required for decomposition of the monofuel is 100 p. s. i. and the orifice area of the respective outlet or exhaust nozzle of each of the said chambers are related in the inverse ratio to the pressure required in each of the chambers. If then the final outlet or exhaust nozzle, that is the nozzle leading to the turbine starter is 7.5 mm. diameter the intermediate nozzle will be approximately 3.75 mm. diameter and the auxiliary chamber exhaust nozzle will be 1.9 mm. diameter. (The sizes of outlet nozzles quoted will give considerably more than the neccssary minimum pressure but any stray losses etc. will be allowed for.)

The auxiliary chamber (the reaction chamber) is raised to decomposition conditions for the monofuel by the heater means and then raised to its full working pressure, 800 p. s. i. At this point the pressure in the intermediate chamber will be suificient to initiate decomposition of its own monofuel supply and this is switched on and the conditions in the chamber can now be raised to full working pressure, 800 p. s. i. With the intermediate chamber at full working pressure the main chamber monofuel supply is switched on and the main chamber brought up to full working conditions. After the main chamber is at full working pressure the auxiliary and intermediate chambers can be switched off if desired, but for some applications it may be an advantage to keep at least the intermediate chamber in action.

in any system using more than two chambers, only the first chamber, the reaction chamber per se, will have a heater.

it can be seen that the problem of starting a prime mover in a short time would be eased if the minimum pressure required for decomposition could be reduced. it has been found that if the intermediate chamber is partially filled with metal foil in a gauze container to act as a thermal mass, the minimum pressure required for decomposition of the monofuel may be considerably reduced. This may be explained by the fact that a certain amount of heat energy is stored in the foil (the foil being heated by the hot gas from the preceding chamber) and when the fuel is switched on, the heat energy is transferred to the fuel, causing evaporation and heating of the resultant gas; a similar action to that which takes place in the chamber with the heating element.

It will further be appreciated that where two or more chambers are employed in a series arrangement with a main reaction chamber the influx of monofuel from the storage tank into any chamber must be controlled with regard to the pressure and temperature existing in the chamber preceding it from which decomposed monofuel will arrive to set up decomposition of the monofuel supplied from the storage tank to that chamber.

The salient features of the invention will be more readily appreciated from the following description, reference being had to the accompanying drawing, which shows an arrangement for starting a turbine starter of a gas turbine.

Referring now specifically to the drawing, a fuel tank 10 holding monofuel has its contents fed via header 30 by a pump 11 and pump motor 12 to a reaction chamber hereinafter termed the auxiliary chamber 13 containing a heater element 14. The feed pipe 15 which connects header 30 to auxiliary chamber 13 contains a solenoid valve A controlling the inlet atomizing nozzle AN, a nonreturn valve R1 and a pressure sensitive switch b sensitive to the pressure within auxiliary chamber 13 is provided. An output nozzle 16 connects the auxiliary chamber 13 via a pipe line 17 with an intermediate chamber 18. The intermediate chamber 18 has its own supply of monofuel via pipe line 19 containing a solenoid valve B controlling an inlet atomizing nozzle Bn and a non-return valve R2. The valve B is actuated from the pressure sensitive switch 15. A pressure sensitive switch 0 sensitive to the pressure within the intermediate chamber 18 is also provided. An outlet nozzle 20 connects the intermediate chamber 18 with a main chamber 21 via a pipe line 22. The main chamber has its own supply of monofuel via pipe line 23 containing a solenoid valve C controlling an inlet atomizing nozzle CN and a non-return valve R3. The valve C is actuated from the pressure sensitive switch c. An outlet nozzle 24 connects the main chamber 21 with the turbine starter, not shown, via pipe line 25. Each pipe line bringing monofuel to a chamber, viz pipes 15, 19, 23 and header 30 may be provided with a flow restrictor 26, 27, 28 respectively, and a non-action valve. The operation of the system is as follows.

Operations I. Motor 12 and pump 11 switched on; heater means 14 switched on.

H. After a predetermined time the heater means 14 is switched off and solenoid valve A is opened. Pressure in auxiliary chamber 13 builds up to full working pressure (e. g. 800 p. s. i.).

IlI. With auxiliary chamber 13 at 800 p. s. i. correct conditions exist to initiate decomposition of monofuel in intermediate chamber 18 and solenoid valve B and nozzle BN are opened by pressure switch b; pressure in intermediate chamber 18 builds up to full working pressure (e. g. 800 p. s. i.).

IV. Conditions are now right to initiate decomposition of monofuel in main chamber 21 and solenoid valve C and nozzle CN are opened by pressured switch 0. Pressure in main chamber builds up to full working pressure (e. g. 800 p. s. i.).

V. Pump 11 shut down after predetermined time interval.

If necessary the auxiliary and intermediate chambers can be shut down by the rise of pressure in the main chamber.

The method of control described above is only one of a number of possible alternative methods, but in each case the principle of initiating decomposition of monofuel in one chamber by means of the hot gas from the preceding chamber would remain the same.

It will be appreciated by those skilled in the art that Whereas the method of starting hereinbefore referred to in reference to the a'fore-described apparatus specifies the use of a monofuel, the starting apparatus is operable with the well known bifuels and the only alteration required is the provision of two storage tanks in place of one.

What we claim as new and desire to secure by Letters iatent of the United States is:

1. In apparatus for starting a prime mover, the combination comprising, a prime mover starter mechanism provided with a gas inlet, a source of supply of a monofuel, a first chamber having an inlet, an outlet and a heating means, a second chamber provided with greater volumetric capacity than said first chamber, which second chamber is provided with first and second inlets and an outlet, a third chamber provided with greater volumetric capacity than said second chamber, which third chamber is provided with first and second inlets and an outlet, combined means connecting said source of supply of a monofuel with said inlet of said first chamber and the first inlets of said second and third chambers, conduit means connecting the outlet of said first chamber with the second inlet of said second chamber, conduit means connecting the outlet of said second chamber with the second inlet of said third chamber, and conduit means connecting the outlet of said third chamber with the gas inlet of said prime mover starter mechanism.

2. In apparatus for starting a prime mover, the combination comprising, a prime mover starter mechanism provided with a gas inlet, a source of supply of a monofuel, a first chamber having an inlet, an outlet, and a heating means and a control device responsive to the pressure within said chamber, a second chamber provided with greater volumetric capacity than said first chamber, said second chamber having first and second inlets, an outlet and a control device responsive to the pressure within said second chamber, a third chamber provided with greater volumetric capacity than said second chamber, said third chamber having first and second inlets and an outlet, first conduit means connecting said source of supply of monofuel with the inlet of said first chamber, second conduit means connecting said source of supply of monofuel with the first inlet of said second chamber, first valve means located in said second conduit means, third conduit means connecting said source of supply of monofuel with the first inlet of said third chamber, second valve means located in said third conduit means, fourth conduit means connecting the outlet of said first chamber with the second inlet of said second chamber, fifth conduit means connecting the outlet of said second chamber with the second inlet of said third chamber, sixth conduit means connecting the outlet of said third chamber with the gas inlet of said prime mover starter mechanism, means to control the actuation of said first valve means by the pressure responsive device of said first chamber, and means to control the actuation of said second valve means by the pressure responsive device of said second chamber.

Parker Nov. 13, 1951 OTHER REFERENCES Journal of the Institute of Fuel, page 143 of June 1947 issue. 

